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SOALR/1043-79/14 



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Solar Energy System 
Performance Evaluation 



HULLCO CONSTRUCTION COMPANY 

SINGLE FAMILY RESIDENCE 

Prescott, Arizona 

May, 1978 through April, 1979 



U.S. Department of Energy 

National Solar Heating and 
Cooling Demonstration Program 

National Solar Data Program 




NOTICE 

This report was prepared as an account of work sponsored by the United States 
Government. Neither the United States nor the United States Department of Energy, nor 
any of their employees, nor any of their contractors, subcontractors, or their employees, 
makes any warranty, express or implied, or assumes any legal liability or responsibility for 
the accuracy, completeness or usefulness of any information, apparatus, product or process 
disclosed, or represents that its use would not infringe privately owned rights. 



This report has been reproduced directly from the best available copy. 

Available from the National Technical Information Service, U. S. Department of 
Commerce, Springfield, Virginia 22161. 



Price: Paper Copy $5.25 
Microfiche $3.00 



SOLAR/1043-79/14 

Distribution Category UC-59 



SOLAR ENERGY SYSTEM PERFORMANCE EVALUATION 



HULLCO CONSTRUCTION 
PRESCOTT, ARIZONA 



MAY 1978 THROUGH APRIL 1979 



MICHAEL W. WESTON, PRINCIPAL AUTHOR 

V. S. SOHONI, MANAGER OF PERFORMANCE ANALYSIS 

LARRY J. MURPHY, IBM PROGRAM MANAGER 



IBM CORPORATION 
150 SPARKMAN DRIVE 
HUNTSVILLE, ALABAMA 35805 



PREPARED FOR THE 
DEPARTMENT OF ENERGY 
OFFICE OF ASSISTANT 
SECRETARY FOR 
CONSERVATION AND SOLAR APPLICATIONS 
UNDER CONTRACT EG-77-C-01 -4049 
H. JACKSON HALE, PROGRAM MANAGER 



TABLE OF CONTENTS 



Section Title Page 

1 FOREWORD 1 

2 SUMMARY AND CONCLUSIONS 3 

3 SYSTEM DESCRIPTION 5 

4 PERFORMANCE EVALUATION TECHNIQUES II 

4.1 Instrumentation and Data Acquisition .... 12 

4.2 Energy Balance Technique 12 

5 PERFORMANCE ASSESSMENT 19 

6 REFERENCES 47 

APPENDIX A DEFINITION OF PERFORMANCE FACTORS AND 

SOLAR TERMS A-l 

APPENDIX B SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS .... B-l 



n 



LIST OF FIGURES AND TABLES 



FIGURE 



TITLE 



PAGE 



1-1 Hullco Construction Solar Energy System 2 

3-1 Hullco Construction Company Solar Energy System 

Schematic 6 

3-2 Interior View of Greenhouse 7 

3-3 System with Summer Shading in Position 8 

3-4 Wood Stove 9 

5-1 Average Monthly Solar Collection Efficiency 25 

5-2 System Performance - Unoccupied Building 27 

5-3 Average Monthly Storage Temperatures 28 

5-4 Average Monthly Greenhouse Wall and Building 

Temperatures 29 

5-5 Greenhouse Wall Temperatures - April 18, 1979 31 

5-6 Average Monthly Comfort Index Values 35 

5-7 Zone 1 Comfort Index 37 

5-8 Zone 2 Comfort Index 38 

5-9 Average Monthly Relative Humidity Levels 39 

5-10 Interior Daily Average Relative Humidity and 

Greenhouse Fan Operating Energy 41 

5-11 Daily Minimum and Maximum Storage Temperatures 

and Comfort Index ..... 42 

5-12 System Performance - December 5-6, 1978 44 

5-13 Interior View of Living Room Area 46 

TABLE TITLE PAGE 

4-1 Hullco Construction System Sensor Locations 13 

5-1 Weather Conditions 20 

5-2 Comparison to Design Performance - Heating Season .... 21 

5-3 System Thermal Performance Summary - Heating Season ... 23 

5-4 Energy Savings 33 

5-5 Comfort Levels 34 



m 



NATIONAL SOLAR DATA PROGRAM REPORTS 

Reports prepared for the National Solar Data Program are numbered under a 
specific format. For example, this report for the Hullco Construction 
system project site is designated as SOLAR/1043-79/14. The elements of 
this designation are explained in the following illustration. 



Prepared for the 

national Solar 

Data Program 



Demonstration Site 



S0LAR/1C43-79/14 



Report Type 
•Designation 



Year 



Demonstration Site Number: 

Each Project site has its own discrete number - 1000 through 1999 
for residential sites and 2000 through 2999 for commercial sites. 

§ Report Type Designation: 

This number identifies the type of report, e.g., 

Monthly Performance Reports are designated by the numbers 01 
(for January) through 12 (for December). 

Solar Energy System Performance Evaluations are designated 
by the number 14. 

Solar Project Descriptions are designated by the number 50. 

Solar Project Cost Reports are designated by the number 60. 

These reports are disseminated through the U. S. Department of Energy, 
Technical Information Center, P. 0. Box 62, Oak Ridge, Tennessee 37830, 



IV 



1 . FOREWORD 

The National Program for Solar Heating and Cooling is being conducted by 
the Department of Energy under the Solar Heating and Cooling Demonstration 
Act of 1974. The overall goal of this activity is to accelerate the 
establishment of a viable solar energy industry and to stimulate its 
growth in order to achieve a substantial reduction in nonrenewable 
energy resource consumption through widespread applications of solar 
heating and cooling technology. 

Information gathered through the Demonstration Program is disseminated 
in a series of site-specific reports. These reports are issued as 
appropriate, and may include such topics as: 

Solar Project Description 

Design/Construction Report 

Project Costs 

Maintenance and Reliability 

Operational Experience 

Monthly Performance 

System Performance Evaluation 

The International Business Machines Corporation is contributing to the 
overall goal of the Demonstration Act by monitoring, analyzing, and 
reporting the thermal performance of solar energy systems through analysis 
of measurements obtained by the National Solar Data Program. 

The System Performance Evaluation Report is a product of the National 
Solar Data Program. Reports are issued periodically to document the 
results of analysis of specific solar energy system operational perform- 
ance. This report includes system description, operational characteris- 
tics and capabilities, and an evaluation of actual versus expected 
performance. The Monthly Performance Report, which is the basis for the 
System Performance Evaluation Report, is published on a regular basis. 
Each parameter presented in these reports as characteristic of system 



performance represents over 8,000 discrete measurements obtained each 
month by the National Solar Data Network. 

All reports issued by the National Solar Data Program for the Hullco 
Construction solar energy system are listed in Section 6, References. 

This Solar Energy System Performance Evaluation Report presents the 
results of a thermal performance analysis of the Hullco Construction 
passive solar space heating system. Analysis covers operation of the 
system from May 1978 through April 1979. The Hullco Construction solar 
energy system provides space heating to a single-family residence (Figure 
1-1) located in Prescott Arizona, using an attached greenhouse as the 
primary solar energy collection area. A more detailed system description 
is contained in Section 3.0. Analysis of the system thermal performance 
was accomplished using measurements and a system energy balance technique 
described in Section 4. Section 2 presents a summary of the results and 
conclusions obtained, while Section 5 presents a detailed assessment of 
the system thermal performance. 




Figure 1-1. HULLCO CONSTRUCTION SOLAR ENERGY SYSTEM 



2. SUMMARY AND CONCLUSIONS 

This system Performance Evaluation Report provides an operational summary 
of the solar energy system at the Hullco Construction site, a single 
family residence located in Prescott, Arizona. This analysis is conducted 
by evaluation of measured system performance and by comparison of measured 
weather data with long-term average climatic conditions. The performance 
of major subsystems is also presented. 

Features of this report include: a system description, a review of 
actual system performance during the report period, analysis of perform- 
ance based on evaluation of meteorological load and operational conditions, 
and an overall discussion of results. 

The Hullco Construction passive solar space heating system satisfied 75 
percent of the building energy requirement during the winter of 1978- 
1979. Wood, as another renewable energy form, provided much of the 
remainder of the energy requirement. Although this performance level is 
slightly below design performance specifications, the differences in 
design and actual performance can be accounted for by both the severe 
winter weather conditions encountered and by facets of owner interaction 
with operation of the system. Comfort levels inside the building were 
acceptable over most of the year, although some comfort-related problems 
were encountered with summer overheating and winter interior humidity 
levels. However, practical solutions to the comfort difficulties have 
been identified so that the problems can be reduced during the next year 
of system operation. Since most of the difficulties encountered were 
related to system operation or control, it is important that the home 
owner have a good awareness of appropriate system control operations. 
The important aspects of system control awareness, along with a detailed 
discussion of the performance and comfort encountered, are presented 1n 
Section 5. 






Digitized by the Internet Archive 

in 2012 with funding from 

University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation 



http://archive.org/details/solarhullco1979 



3. SYSTEM DESCRIPTION 

The Hullco Construction solar energy system [1]* is a passive space 
heating system for a single-family residence located in Prescott, Arizona. 
The 1,056 square foot, south-facing building, illustrated in the drawings 
of Figure 3-1, is a combination greenhouse and direct gain passive system. 
Incident solar energy enters the building through approximately 400 square 
feet of double-glazed prefabricated Kalwall panels. Two sliding glass 
doors between the greenhouse and the house, along with a window in the 
bathroom, admit incident solar energy directly into the master bedroom, 
living room, and bath areas of the house. Collected solar energy which 
is not used to satisfy the immediate building space heating demand is 
stored directly in the massive walls and floors of the building or in- 
directly in the 670 cubic feet of 3 to 5 inch diameter rock storage 
located under the floor of the north half of the building. Stored energy 
is released by low- temperature radiation and convection to satisfy the 
building space heating demand during periods of time when incident solar 
energy is not available. 

Direct storage of collected solar energy is provided by the walls and 
floor of the building. The brick floor and the black painted north wall 
of the greenhouse (Figure 3-2) provide solar energy storage for the 
greenhouse. The 12-inch thick, sand-filled concrete block greenhouse 
north wall acts as a Trombe wall, storing collected energy from the 
greenhouse during the day and releasing the collected energy by radiation 
to the south part of the building at night. The 4-inch thick building 
concrete slab floor acts as direct solar storage, particularly in the 
living room and master bedroom areas where the floor is covered with 
Mexican tile masonry. Additional storage is provided by the 8-inch 
thick, solid grouted, concrete exterior insulated building walls on the 
north, east, and west perimeter of the building. 

Indirect storage of collected solar energy is provided by the 670 cubic 
feet of rock storage located under the north side of the building and by 
the 4-inch thick carpeted concrete slab floor poured on top of the rock. 



Numbers in brackets [ ] denote reference numbers in Section 6. 




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BEDROOM 



MASTER 
BEDROOM 



BEDROOM 



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KITCHEN 



LIVING 




GREENHOUSE 



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ZONE 2 



ZONE 1 



( PLAN VIEW ) 



SOUTH 



GREENHOUSE, 











FLOOR USED AS 
STORAGE 



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STORAGE 
WALL 



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ROCK BED STORAGE ,;/: '" 



SECTION VIEW 



Figure 3-1. HULLCO CONSTRUCTION COMPANY SOLAR ENERGY SYSTEM SCHEMATIC 



Solar energy collected in the greenhouse is transferred to the rock bed 
from vents at the top of the greenhouse through under- floor ducts by two 
one-third horsepower blowers located at the east and west ends of the 
greenhouse shown in Figure 3-2. After transferring energy to the rocks, 




Figure 3-2. INTERIOR VIEW OF GREENHOUSE 

the air returns to the greenhouse through the house from floor vents lo- 
cated at the north side of the building. The greenhouse fans operate when 
temperatures near the top of the greenhouse reach approximately 90°F. 
Energy stored in the rock is released through the carpeted concrete floor 
to the house. 



Summer overheating protection is provided by venting of the greenhouse 
and by both natural and artificial shading of the greenhouse glazing. 
Natural shading of the greenhouse is accomplished by the use of an 



existing tree to the southeast of the structure. However, the tree, a 
Juniper, does shade the greenhouse some during the mornings during the 
heating season. Additional greenhouse shading can be provided by a redwood 
snow fence placed over the glazing (Figure 3-3). Draperies covering the 




Figure 3-3. SYSTEM WITH SUMMER SHADING IN POSITION 

sliding glass doors on the north wall of the greenhouse can be closed to 
prevent Incident sunlight from entering the building. Nighttime venting 
of the building can be used to cool the energy storage masses, thus allowing 
the building to be cooled during the day as energy generated inside the 
building is absorbed by the walls and floor. Daytime venting of the 
greenhouse is accomplished using a thermostatically controlled powered fan 
located at the top of the greenhouse to draw air through the house and out 
at the top of the greenhouse. 



Low building heating loads are maintained by the use of good energy con- 
servation construction techniques. The north, east, and west walls are 
insulated on the outside of the concrete blocks with two inches of 



styrofoam to yield a total wall R-value of 11. Nine inches of fiberglass 
batt insulation is used in the roof to yield a roof R-value of 32. The 
entire perimeter of the concrete slab floor is insulated. A minimum of 
window area is used on the north, west, and east walls. The building is 
bermed four feet into the earth on the north and west sides. 

Auxiliary energy for space heating can be supplied by either electric 
radiant heat panels or by the wood-burning stove located in the living 
room (Figure 3-4). The stove uses outside air for combustion. The 




Figure 3-4. WOOD STOVE 

ceiling-mounted electric radiant heat panels located in each room are 
controlled by individual room thermostats. 



The predicted annual solar contribution to the building load is 80 
percent. Design monthly building heating loads, including the greenhouse 
load, are approximately 11,000 Btu per heating degree-day. 



A non-instrumented thermosyphoning hot water system is used to provide 
domestic hot water preheating. The collector panel for the hot water 
system is located immediately behind the center panel of the greenhouse, 
with the preheat tank located in the greenhouse immediately above the 
collector. Hot water is preheated in the tank, and passes on demand to 
the hot water heater where it is raised to operating temperature. 



10 



4. PERFORMANCE EVALUATION TECHNIQUES 

The thermal performance of the Hullco Construction solar energy system 
is evaluated using data from monitoring instrumentation located at the 
site. Performance factors which represent the thermal performance of 
the system are computed using this measurement data. Definition of the 
performance factors used follows the general outlines of the intergovern- 
mental agency report, "Thermal Data Requirements and Performance Evalua- 
tion Procedures for the National Solar Heating and Cooling Demonstration 
Program," [2]. The analysis technique used is outlined in another report, 
"Performance Evaluation Reporting for Passive Systems," [3]. This section 
addresses the application of the passive system thermal performance evalua- 
tion technique to the Hullco Construction system along with a description 
of the measurements used to monitor the system performance. 



11 



4. 1 Instrumentation and Data Acquisition 

Measurement data is provided for analysis using the IBM-developed Central 
Data Processing System (CDPS), [4]. Data from sensors is sampled approxi- 
mately once each five minutes by a microprocessor controlled device lo- 
cated at the site and recorded on cassette tape. Approximately once per 
day a processor at the CDPS automatically accesses the site located 
microprocessor via telephone to collect the data stored on tape. This 
data is further processed by another computer to provide the measurement 
data in a form compatible with both visual and automated data analysis 
procedures. The measurement data is scanned by an analyst, either in 
tabular or plot form, on a frequent basis in order to detect significant 
changes in solar energy system or instrumentation/data acquisition 
system operation. The measurement data is also available to software 
which provides for the computation of the performance factors discussed 
in the remainder of the report. 

System thermal performance at the Hullco Construction site is monitored 
using 70 different measurements of conditions at the site. The monitor- 
ing measurements sampled at the site are summarized in Table 4-1. The 
measurement identification number used in Table 4-1 follows the system 
defined in Reference [2]. The prefix I is used for insolation measure- 
ments, T for temperature measurements, EP for electrical power, W for 

air or liquid flow, V for wind velocity, and D for switches or wind 

2 
direction. Units used for the measurements are Btu/ft -hr for insolation, 

°F for temperature, kilowatts for electric power, feet per minute for 

air flow, miles per hour for wind speed and degrees for wind direction. 

4.2 Energy Balance Technique 

The basis for the analysis technique is an energy balance concept developed 
for use in the National Solar Data Network. All significant sources of 
energy entering and leaving the system, along with the change in energy 
inside the system, are accounted for. The details of the derivation of 



12 



TABLE 4-1. HULLCO CONSTRUCTION SYSTEM SENSOR LOCATIONS 



MEASUREMENT 
IDENTIFICATION 



DESCRIPTION 



IOOl 

T001 
EP100,EP101 

T100.T101 

W100.W101 

RH600 

RH601 

D002 

T200,T201,T202 
T203,T204,T205 
T206,T207,T208 



T209,T210,T211 
T212,T213,T214 
T215.T216J217 

D001 

V001 

EP400.EP401 
EP402,EP403 

T218,T219,T220 
T224,T225,T226 



Incident solar energy normal to the plane of the 
greenhouse glazing. 

Outside ambient temperature. 

Power used by the greenhouse to rock storage blower 
motors. 

Temperatures in the greenhouse at the entry to the 
ducts to the rock storage. 

Air flow rate through the greenhouse to rock stor- 
age ducts. 

Interior relative humidity, measured in the living 
room. 

Outside relative humidity. 

Thermal switch used to indicate wood stove operation 

Rock bed temperatures at three locations on the 
northeast side of the building: three sensors are 
located two inches from the top of the slab, three 
sensors are located in the rock 11 inches from the 
slab top, and the remaining three sensors are loca- 
ted 20 inches down from the top of the slab. 

Rock bed temperature sensors located on the north- 
west side of the house at 2, 11, and 20 inches down 
from the top of the slab. 

Wind direction. 

Wind speed. 

Measurements of the power used by the radiant elec- 
tric heaters used for auxiliary heating. 

Measurements of the greenhouse floor temperature 
near the surface, above the vapor barrier, and 
below the vapor barrier on the east and west sides 
of the greenhouse. 



13 



TABLE 4-1. (Continued) 



MEASUREMENT 
IDENTIFICATION 



DESCRIPTION 



T221,T222,T223 
T227,T228,T229 
T245,T246,T247 

T230,T231,T232 



T233.T234 
T235,T236 
T237.T238 
T239.T240 



T241,T242,T243, 

T244 

T600,T601,T602 
T603.T604 



Measurements of floor surface temperature, below 
slab temperature and earth temperature in the living 
room and the master bedroom. 

Temperatures in the wall between the house and 
greenhouse near both surfaces and in the center 
of the wall . 

Temperatures near the inside and outside surfaces 
of the east building wall. 

Temperatures near the inside and outside surfaces 
of the north building wall. 

Temperatures near the inside and outside surfaces 
of the west building wall. 

Temperatures near the inside and outside surfaces 
of the west greenhouse wall. 

Air temperatures at the outlets of the rock stor- 
age on the north side of the house. 

Ambient air temperatures inside the building in 
bedroom 1, bedroom 2, the master bedroom, the bath 
and hall, and the living room. 



14 



the technique used are presented in References [3] and [5]. The equations 
used are listed in Appendix B of this report. 

The space heating load used in this report and in References [6] - [18] 
is the building load minus the other sources of energy generated inside 
the building which would cause a reduction in the equipment load of an 
active solar energy system or a conventional heating system. As such 
there may be periods of time when significant amounts of energy are 
supplied to the building from renewable energy sources other than solar 
energy. Consequently there may exist periods of time when the reported 
load appears small in relation to the building load since the reported 
load is actually an equivalent equipment demand. 

Using the energy balance concept, the solar energy used is found as the 
difference between the space heating load and the auxiliary energy sup- 
plied to the building. Both the load and the solar energy used represent 
the energy requirements of the building being analyzed and include the 
energy which is lost back through the solar glazing area. All other 
primary performance factors, including energy savings, are computed with 
respect to these load and solar energy used values (Appendix B.) following 
the guidelines of Reference [2]. However, the energy savings, particularly 
when used for comparison with another solar energy system, can be misleading 
if a comparison is made between a passive system analyzed by this technique 
and an active system. Consequently, other energy savings comparisons 
must be made. 

The building savings, or the energy savings for the system as built, are 
presented first. The building savings is the difference between the 
energy required to maintain the measured building interior environment 
and the auxiliary energy used. As such, the building savings represents 
the difference between the homeowner's utility bills with and without 
the use of incident solar energy. 

The second savings is the comparison savings. The comparison savings 
represents the difference between the energy which would be required to 
maintain the measured interior environmental conditions in a comparison 



15 



building and the auxiliary energy used by the system. The comparison 
building is a building which has thermal characteristics identical to 
the passive system on all exterior surfaces except the glazed south 
wall area. For the comparison building load determination, the solar 
glazing is replaced by a wall with thermal characteristics similar to 
the other passive system building walls. Thus, the comparison savings 
represent the savings realized by comparison to a building with the same 
energy conservation characteristics which does not make use of incident 
solar energy for heating. In effect, the comparison savings is the 
building savings reduced by the high losses through the glazed south 
area on a passive system. 

The third savings, the comparison set point savings, is the energy savings 
compared to the energy requirements of the comparison building under condi- 
tions when the temperature inside the comparison building is controlled to 
a set point. This would be the case if a conventional heating system was 
used for control of the building environment. To determine the comparison 
set point savings, a two degree range of building temperature, from 68°F to 
70°F, is used as the set point. When the building temperature is below 
the lower set point temperature of 68°F, the comparison set point savings 
is reduced by the additional energy which would be required to maintain 
the lower set point temperature in the comparison building. Although 
this energy would not decrease the actual savings, it is applied as a 
penalty to the comparison savings for convenience, rather than creating 
a new performance factor. When the building temperature is above the 
upper set point temperature of 70°F, the assumption is made that the 
additional energy used to maintain the higher temperature is excess 
energy. Consequently, the comparison set point savings are reduced 
by this excess energy unless all or part of this excess energy was 
derived from a renewable energy source such as wood. If the excess 
heating energy requirements could be satisfied totally from the other 
renewable energy sources, then no reduction in the solar comparison set 
point savings is made. Otherwise, the savings are reduced by the differ- 
ence between the excess energy and the other source of renewable energy 
(wood). 



16 



Presentation of the three values of energy saved allows the reader to 
observe the effect of more constrained operation of the passive space 
heating system through successively more severe constraints. It should 
be noted that both the comparison savings and the comparison set point 
savings for a well designed and well built passive system will be 
relatively low. However, if the use of auxiliary energy is also low, 
then the relatively low magnitude of the savings reflect only the energy 
conservation features of the system. For a building where the glazing 
is an integral part of the building (i.e., a direct gain system) the 
comparison savings most adequately describe the energy savings realized. 
However, as the glazing and area of collection becomes more isolated 
from the living space, the building savings become more meaningful. A 
greenhouse is in between — that is, it is a livable part of the building 
when greenhouse temperatures are high, but less usable when temperatures 
are lower. Consequently, both the building savings and the comparison 
savings have periods of applicability for the greenhouse system. No 
attempt is made in this report to quantify the energy savings resulting 
from the application of energy conserving construction techniques. That 
is, the energy savings presented in the report are savings resulting 
only from the use of the incident solar energy. 

More complete definitions of the performance factors used for system 
analysis are presented in Appendix A. The equations used to generate 
these performance factors for the Hullco Construction system are presented 
in Appendix B. 



17 



5. PERFORMANCE ASSESSMENT 

During the winter of 1978 - 1979, the solar space heating system satisfied 
75 percent of the building heating load and 100 percent of the subsystem 
space heating demand. The actual performance was slightly below the 
design performance specifications due to the unusually severe winter 
weather. However, significant amounts of energy were saved, even as 
compared to a more conventional style of building construction. Comfort 
levels were within an acceptable range over most of the year. High 
building temperatures encountered during the summer months could have 
been prevented by more appropriate use of system controls. A problem 
with excess interior humidity has existed, but also can be corrected by 
appropriate use of system controls. 

Climatic conditions in the Prescott area during the time period covered 
by this analysis, as shown in Table 5-1, were such that both winter 
heating and summer cooling loads were more severe than in a typical 
year. While summer outside ambient air temperatures were near the long- 
term average, the amount of solar energy incident on the greenhouse 
glazing was 10 to 15 percent higher than the long-term average, particu- 
larly during the late spring and early summer months. Both the outside 
ambient temperature and the available solar energy were much less than 
normal during the winter, particularly during the month of January, 
contributing to the more severe heating requirements encountered. 
Average measured monthly values of wind speed were near three miles per 
hour for each month. However, during all seasons except the fall, average 
daily wind speed frequently exceeded 5 miles per hour and occasionally 
exceeded 10 miles per hour. Outside relative humidity averaged slightly 
over 50 percent for the year. However, the average values during both 
spring and summer were relatively low, while late fall and early winter 
values were quite high, averaging near 70 percent. 

Design predictions of the system thermal performance, shown in Table 5-2 
along with actual system thermal performance, were made using a degree- 
day technique. Assumptions made in the design performance calculations 
included: 



19 



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21 



» Design -indoor temperature of 65°F in the winter 
a An Infiltration rate of outside air of one-half air 

change per hour 
• Climatic conditions shown as long-term average in Table 5.1. 

As can be seen from a comparison of the design and actual solar frac- 
tions of the building heating load shown in Table 5-2, the heating 
season performance fell well below the design estimates. However, since 
the outside air temperature was cooler than the design temperature and 
the inside air temperature was maintained considerably above the design 
temperature of 65°F, then the actual building heating loads shown in 
Table 5-2 were considerably higher than the design values. The higher 
building loads, along with the lower than average available solar 
energy caused the majority of the differences in the design and actual 
solar fractions. However, even after the differences in temperature are 
accounted for, the actual load remained higher than the design load. This 
was due to differences between the design infiltration rate of one-half 
air change per hour and the actual infiltration rate which averaged one 
to one and one-half air changes per hour. The building appears to be 
tightly weatherized, thus justifying a design infiltration rate of one- 
half air change per hour. The higher actual outside air infiltration 
rate appears to have been caused not by building design, but by the way 
the system was operated. Relative humidity levels inside the building were 
high enough during the winter to cause some discomfort to the occupants 
and to cause some mildew to occur inside the building. In an attempt to 
reduce the interior humidity level, the occupants would frequently open 
the building windows a small amount to allow the dry outside air to 
enter the house during daytime hours. As a consequence of the slightly 
open windows, the average infiltration rate was higher than the design 
rate. The causes of the high interior relative humidity will be discussed 
in later paragraphs. 

A month-by-month summary of the Hullco Construction passive solar space 
heating system thermal performance is shown in Table 5-3. As discussed 
earlier, the building loads were considerably higher than expected. How- 
ever, nearly 100 percent of the building heating load was satisfied by 
renewable energy forms - wood and sunlight. Since the internal heat 

22 



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23 



gains are always present in an occupied building, then the solar fraction 
of the building load can never reach 100 percent in an occupied building. 

During the winter, the wood stove was used on many days to maintain com- 
fortable conditions inside the building. A total of 13.51 million Btu of 
useful thermal energy was derived from use of the wood stove during the 
winter. According to the occupants, approximately one and one-half cords 
of wood were used during the winter. Assuming a heat content of 30 
million Btu per cord of wood, then the wood stove operation provided 
energy at an average efficiency level of 30 percent. The wood stove was 
used primarily to maintain a lower bound to the building temperature 
and interior comfort level. Thus, the majority of the wood stove use 
occurred at night through early morning hours and during cloudy days. 

Other energy used to satisfy the building load was derived from electric 
lights, appliances, etc., including the greenhouse fans, and from the 
body heat of the occupants. This internal heat gain over the winter 
is estimated to be 5.67 million Btu. 

For reporting purposes, the reported load is an equivalent equipment 
demand. As illustrated in Table 5-3, this space heating equipment demand 
is the difference between the building load and the sum of the wood and 
internal energy gains. This demand is the amount of energy which would be 
required to maintain the measured building environmental conditions. Al- 
most 100 percent of this space heating subsystem demand was satisfied by 
collected solar energy. Only 0.04 million Btu (11 kwh) of auxiliary 
electric fuel was used over the entire heating season. 

The primary collection of incident solar energy at the Hullco Construction 
site occurs in the greenhouse. Energy collected in the form of warmed 
air, walls, or floors is transferred to the remainder of the house by 
both active (fans) and passive or natural means. The efficiency of this 
collection is illustrated in the plot of average monthly collection ef- 
ficiency presented in Figure 5-1. As can be seen from the plot, the 



24 




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(±N3Dd3d) ADN3IOIdd3 N0I1D3110D 



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25 



efficiency reaches a maximum near the coolest part of the year (mid-winter) 
and drops off rapidly in the fall and spring when shading and venting to 
control overheating reduce the efficiency of energy collection. Of par- 
ticular interest is the plot of the two months (March and April) of 1978, 
as compared to the corresponding period of 1979. During the spring of 
1978 the house was unoccupied. The house was occupied in late May of 1978. 
Consequently, minimum overheating control in the form of manual shading 
and venting was accomplished. As a result, higher collection efficiencies 
were observed during the two months of 1978. It should be noted that the 
value of collection efficiency does not directly compare to the collection 
efficiencies presented for active solar energy systems, since the thermal 
losses through the passive system glazing are a part of the building load 
instead of a part of the collection efficiency. 

Storage of collected solar energy at the Hullco Construction site is 
provided by building floors, walls, and the under floor rock bed. The 
storage provided several days reserve heating on a number of occasions 
throughout the winter while also aiding in moderation of daily temperature 
variations within the conditioned space, as illustrated by the plot in 
Figure 5-2 showing average building and storage temperatures during a 
two-day winter period when the building was unoccupied. The effect of 
the greenhouse fan operation on building temperature is apparent during 
both days as a change in the rate of change of building temperature with 
time. Of the three areas of storage (wall, floor, rocks) the wall 
between the house and greenhouse, a primary absorbing area for incoming 
solar radiation, was the primary solar storage media. Referring to the 
plot of monthly average storage temperatures presented in Figure 5-3, 
it can be seen that the wall is generally five or more degrees warmer 
than the floor or the rocks, thus indicating that the wall is the primary 
storage media. It should also be noted that the floor provided good 
secondary storage, since its temperature was consistently near or above 
70°F. As shown in Figure 5-4, the greenhouse wall was consistently 
maintained at a higher temperature than the building average tempera- 
ture, thus providing energy to the house. 



26 




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29 



The greenhouse wall also acted as a Trombe wall in its daily cycle of 
operation. Referring to the one-day plot of wall temperatures presented 

Figure 5-5, it can be seen that the temperature of the outer (oreen- 
house) side of the wall varies significantly, from a low near 65°F early 
in the morning to a high near 90°F late in the afternoon. However, the 
wall temperature at the center exhibits less variation, while the house 
side of the wall exhibits still less variation (less than 5°F). Thus 
the thickness of the wall provides a moderation of the temperatures from 
outside to inside, such that the energy in the wall is more evenly 
available to the house ever the entire day. 

The thickness of the wall also provides a time lag to the energy availa- 
bility to the house. From mid-morning through late afternoon, when 
solar energy is available through the sliding glass doors in direct gain 
form, the inside of the greenhouse wall is at its lowest temperature. 
However, at some time after sunset, the inside of the greenhouse wall 
reaches its maximum temperature, and continues to remain at a higher 
temperature than the outside of the wall, thus providing a time lag in 
the energy availability to the house. 

The under floor rock storage appears to have provided little benefit to 
the system thermal performance. In terms of storing energy and releasing 
it for later use, the rocks were seldom warm enough to provide useful 
heating to the building. Only in November did the average rock tempera- 
ture even approach the direct gain floor average temperature. Consequen- 
tly, the rock storage served principally as a thermal buffer to the 
outside environment, and not as an effective thermal storage area. Near 
the end of December the greenhouse fans were disabled and remained off 
until February 10. Consequently, during this period and after the 
greenhouse fans were enabled, the rock storage was rather ineffective 
from a thermal standpoint, since the rock temperature was lower than the 
building temperature. 

As discussed in section 3, the control thermostats for the greenhouse 
fans were set such that operation of the greenhouse fans occurred when 



30 




ii S33UD3Q) 3aniVd3dW31 



1 



31 



greenhouse temperatures exceeded 90°F. The thermostats are manually 
adjustable. If the thermostats had been set at a lower level, i.e., 
80°F, then fan operation would have occurred over longer periods, causing 
more energy to be transferred from the greenhouse to the rock beds. 
Further discussion of the effects of the greenhouse fans on comfort is 
contained in later paragraphs. 

Energy savings realized by the system throughout the heating season, as 
presented in Table 5-4, were substantial, even as compared to more 
conventional construction (comparison and comparison set point savings). 
Operation of the greenhouse fans consumed only 1.07 million Btu of 
electrical energy. Total energy savings for the heating season were 
16,798 kwh for the building, 9,506 kwh as compared to a building of 
similar design but with an insulated non-glazed south wall with thermal 
properties similar to the other building walls, and 6,747 kwh as compared 
to the conventional building where temperatures were controlled to a set 
point. Of particular interest is the month of October, where the compari- 
son set point savings are zero, while other savings are greater than 
zero. This is due to the building temperature being eight degrees 
higher than the upper set point. 

Comfort conditions inside the building were marginally acceptable to the 
occupants during most of the year. Average monthly differences between 
Zone 1 and Zone 2 comfort indices, shown in Table 5-5, were generally 
less than two degrees, indicating good north-south energy transfer 
within the building. During late December through early February, 
however, a more significant difference (Figure 5-6) in the two comfort 
levels was noticed since the greenhouse fans were disabled over the 
entire month, resulting in cooler rock bed temperatures. Summer comfort 
levels were somewhat high, primarily due to the effect of the wall 
between the house and the greenhouse. Even though both the greenhouse 
and house were vented some during the summer, incident sunlight still 
caused considerable heating of the wall, as shown in the plot of storage 
temperatures presented in Figure 5-3. Consequently, the massive wall 
retained a substantial amount of collected solar energy and caused the 



32 



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35 



building, particularly on the south side, to be significantly warmer 
than prevailing ambient conditions. 

The comfort index used in this analysis is the operative temperature, 
which is defined as the average of the space dry bulb and mean radiant 
temperatures. For this analysis, the space mean radiant temperature is 
defined as the average surface temperature of all radiating surfaces 
bordering the space, except the wood stove, since a surface temperature 
measurement of the wood stove is not currently available. The building 
is divided into two comfort zones. Zone 1 is the south part of the 
building, while Zone 2 is the north part of the building. While relative 
humidity does play an important part in the perception of comfort, it is 
not presently included in the comfort index. The effects of humidity on 
comfort will, however, be discussed in later paragraphs. 

An indication of the variation of conditions inside the building is 
shown in Figures 5-7 and 5-8 where, in addition to the average monthly 
values of the comfort index, the average of the daily maximum and 
minimum values is shown. The difference in the average variations 
is generally five degrees or less for both zones. Minimums in 
Zone 1 seldom were less than 70°F due to both the warming effect of 
the wood stove and the efficient radiant and convective energy transfer 
from the greenhouse wall. However, minimums of the Zone 2 comfort index 
were frequently below 70°F, especially when the greenhouse fans were not 
operating (late December through early February). This is due to rela- 
tively inefficient fan-off energy transfer from the greenhouse to the 
north side of the building, particularly to the two north side bedrooms. 

The greenhouse to rock storage fans were disabled by the occupants 
during late December and remained off until February 10. This was due 
to the occupants' perception that operation of the fans was causing an 
increase in interior relative humidity and a consequent decrease in 
their comfort. Examination of the monthly average values of both exterior 
and interior relative humidity, shown in Figure 5-9, reveals a consider- 
able increase in interior relative humidity during November. This 



36 




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39 



increase would appear to be caused by the corresponding increase in 
outside relative humidity. However, even though the outside relative 
humidity level increased substantially during November, the outsiue 
ambient temperature decreased to a monthly average of 42 C F so that the 
absolute humidity of the outside air actually decreased. The decreased 
outside absolute humidity was equivalent to an interior relative humidity 
of approximately 20 to 25 percent at a temperature of 70°F. 

Further examination of Figure 5-9 shows that there was a decrease in 
interior relative humidity noted during the month of January when the 
greenhouse fans were disabled, thus indicating a possible correlation 
between the greenhouse fan operation and interior relative humidity. 
Proof of this effect is contained in the plots presented in Figure 5-10, 
where daily values of interior relative humidity and greenhouse fan 
operating energy are plotted. As can be seen from the plots, definite 
increases in interior relative humidity are noted when the greenhouse 
fans operate. Also, during both the period before January and the 
period after January, a slight increase in the relative humidity with 
time is apparent. The increase in relative humidity during the greenhouse 
fan operation could be due to either high humidity in the greenhouse air 
from plant transpiration and watering of the plants, or due to water in 
the rock bins, although the most probable cause is high humidity in the 
greenhouse air. 

Further effects of the greenhouse fan operation can be seen in the plots 
presented in Figure 5-11, illustrating the daily maximum and minimum of 
both the average storage temperature and the comfort index for both 
building zones. The greenhouse to rock bed fans were disabled from 
December 26 through February 9. During this period, minimum values of 
the comfort index remained near minimum values seen in other periods due 
to the use of the wood stove. However, maximum values, particularly 
near the end of the fan-off period, were considerably higher than previ- 
ously noted. Also, as seen in the storage temperatures, another effect 
of disabling the fans was to reduce the system storage capacity, thus 
reducing the levels of energy, and consequently temperatures in storage, 



40 







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42 



since the north floor rock storage was no longer being charged. This 
reduction of storage capacity is also reflected in the higher day-to-day 
variation of maximum comfort index values, since less effective energy 
storage mass was available to temper the effects of changing daily 
weather conditions. 

Insight into the svstem performance during a day is provided by the 
plots presented in Figure 5-12. During the 2-day period illustrated 
(December 5-6, 1978), considerably more solar energy was available 
during the first day than the second day. Building hourly average 
temperatures were maintained within a range of 69.5°F to 76°F on December 
5, while storage temperatures, particularly in the greenhouse wall, 
varied considerably. Building average temperatures on December 6 were 
slightly cooler until late in the afternoon, when wood stove operation 
was noted. Until the wood stove operation began on December 6, building 
temperatures decayed slowly due to both the small amount of available 
solar energy and the energy released from storage. The direct gain 
floor began to become more effective as an energy storage mass as it 
dropped slightly in temperature and energy level on the 6th. Relative 
humidity effects, as previously discussed, were noted on December 5 
corresponding to the period of operation of the greenhouse fans. However, 
a considerable decrease in interior relative humidity was noted on 
December 6, when wood stove operation began, indicating the increased 
infiltration of outside air (low moisture content) necessary to provide 
combustion air for the wood. 

The two major difficulties encountered during the year, as previously 
discussed, were comfort related difficulties. Both problems could have 
been alleviated by changes to the method of operation of the system. 
The overheating in the summer could have been better controlled by both 
proper venting of the building and appropriate use of greenhouse shading 
devices. The high interior relative humidity was reduced some by winter 
building venting, but at the expense of increased building load. The 
relative humidity increases could have been eliminated by controlling 
the air flow such that it would pass through the rock bins but not 
return through the building. 

43 



WOOD 
STOVE ON 




DEC 5 



24 



DEC 6 



Figure 5-12 SYSTEM PERFORMANCE-DECEMBER 5-6, 197S 



44 



Control of the conditions inside a passively-heated building is an 
extremely important aspect of the system operation. In general, the 
controls applied in the form of venting and shading must be somewhat 
anticipatory in nature - that is, the occupants must begin to change 
system control strategies in advance of seasonal weather changes (spring 
and fall). This was not done at the Hullco Construction site for the 
summer of 1978, primarily because the building was unoccupied during the 
spring. A more appropriate control strategy is to begin in the spring 
to try to keep the thermal storage masses at as low a temperature as 
possible by venting the house to the cool spring air and by applying 
shading controls early in the season. If the storage masses can enter 
the summer cooling season at a lower temperature, then they can be much 
more effective in reducing high daytime temperature levels by absorbing 
more energy during the day. Also, venting of the greenhouse should 
begin as early as possible to try to maintain lower temperatures in the 
greenhouse. With the occupants aware that this type of control is 
necessary then the summer of 1979 should yield significantly lower 
system temperatures. 

In the same vein, control strategies for winter operation should be 
entered as early in the fall as possible, thus providing a "fully charged" 
system for heating season operation. This was accomplished in 1978 due 
to two factors. First, high temperatures were maintained inside the 
house due to greenhouse operation and improper use of system venting. 
Second, the redwood snow fence used to provide partial greenhouse shading 
was not used until late in the summer; thus, the system and its storage 
masses were "fully charged" in anticipation of winter heating demands. 

Another factor contributing to potential overheating is the placement of 
furniture and rugs in the direct gain areas of both the living room and 
the master bedroom. During the spring of 1979, furniture and rugs were 
placed over the mexican tile floor in both rooms, as shown in Figure 5-13. 
Consequently, energy entering through the sliding glass doors was absorbed 
in material with little thermal storage capacity, causing the material 



45 




Figure 5-13. INTERIOR VIEW OF LIVING ROOM AREA 

(furniture, rugs, etc.) and the surrounding air to warm rapidly and con- 
tribute to larger daily temperature variations within these rooms. 

The high relative humidity inside the house during the winter can be 
eliminated by removing the cause; that is, by causing the air from the 
rock beds to return to the greenhouse without entering the house. Since 
the rock beds are continuous from east to west, then the rock bed can be 
charged by only one greenhouse fan. By closing the floor vents on the 
north side of the building, the return air to the greenhouse will be 
ducted through the other side greenhouse fan ducts. Thus, the humid air 
will pass only through the rocks and not through the house. If the 
operating fan control thermostat is set lower (near 80°F), then signifi- 
cant greenhouse overheating should not occur. 

From the discussions of the preceding paragraphs, it can be seen that 
owner interaction with the system is quite important, particularly in 
the area of maintaining appropriate comfort conditions. Although the 
appropriate system controls are not complex and do not require significant 
effort, the homeowner must be made aware of the type of controls he has 
over his system, and how he should anticipate seasonal weather changes 
in their application. Without this owner awareness, the best designed 
and built passive heating system can produce an environment that is only 
marginally comfortable at best. 
46 



6. REFERENCES 

1. "The Hull Residence: A Passive Solar Hybrid System", proceedings 
of the 2nd National Passive Solar Conference, March 16-18, 1978, 
Philadelphia, Pennsylvania. 

2. "Thermal Data Requirements and Performance Evaluation Procedures 
for the National Solar Heating and Cooling Demonstration Program", 
NBSIR 76-1137, Washington: National Bureau of Standards, August, 
1976. 

3. *"Performance Evaluation Reporting for Passive Systems", April 17, 

1979, SOLAR/0018-79/35. 

4. *U. S. Department of Energy, "National Solar Data Network," prepared 

under Contract Number EG-77-C-01-4049, by IBM Corporation, December, 
1979. 

5. A Thermal Performance Analysis Technique for Passive Solar Space 
Heating Systems" proceedings of the 3rd National Passive Solar 
Conference, January 11-13, 1979, San Jose, California. 

6. *"Monthly Performance Report, Hullco Construction", March 1978, 

SOLAR/1043-78/03 

7. *"Monthly Performance Report, Hullco Construction", April 1978 

SOLAR/1043-78/04 

8. *"Monthly Performance Report, Hullco Construction", May 1978, 

SOLAR/1043-78/05 



* Copies of these reports may be obtained from Technical Information 
Center, P. 0. Box 62 Oak Ridge, Tennessee 37830 



47 



9. *"Monthly Performance Report, Hullco Construction", June 1978, 

SOLAR/1043-78/06 

10. *"Monthly Performance Report, Hullco Construction", August 1978, 

SOLAR/1043-78/08 

11. *"Monthly Performance Report, Hullco Construction", September 1978, 

SOLAR/1043-78/09 

12. *"Monthly Performance Report, Hullco Construction", October 1978, 

SOLAR/1043-78/10 

13. *"Monthly Performance Report, Hullco Construction", November 1978, 

SOLAR/1043-78/11 

14. *"Monthly Performance Report, Hullco Construction", December 1978, 

SOLAR/1043-78/12 

15. *"Monthly Performance Report, Hullco Construction", January 1979, 

SOLAR/1043-79/01 

16. *"Monthly Performance Report, Hullco Construction", February 1979, 

SOLAR/1043-79/02 

17. *"Monthly Performance Report, Hullco Construction", March 1979, 

SOLAR/1043-79/03 

18. *"Monthly performance Report, Hullco Construction", April 1979, 

SOLAR/1043-79/04 

19. *"User's Guide to the Monthly Performance Report of the National Solar 

Data Program," February 28, 19,78, SOLAR/0004-78/18. 



* Copies of these reports may be obtained from Technical Information 
Center, P. 0. Box 62, Oak Ridge, Tennessee 37830 



48 






APPENDIX A 

DEFINITION OF PERFORMANCE FACTORS AND SOLAR TERMS 

This section contains the definitions of performance factors used in the 
Hullco Construction monthly reports (References [6] - [18]). Those per- 
formance factors used to describe the thermal performance of solar energy 
systems are described in Reference [19]. 

SITE SUMMARY 

The overall system performance is characterized by monthly summations and 
averages of appropriate daily and hourly performance factors. 

t INCIDENT SOLAR ENERGY (SEA) is the total insolation available 
on the gross collector array area. This is the area of the col- 
lector energy-receiving aperture, including the framework, which 
is an integral part of the collector structure. 

• COLLECTED SOLAR ENERGY (SECA) is the thermal energy removed 
from the collector array by the heat transfer medium. 

• AVERAGE AMBIENT TEMPERATURE (TA) is the average temperature of 
the outdoor environment at the site. 

• AVERAGE BUILDING TEMPERATURE (TB) is the average temperature in 
the controlled space of the building which the system serves. 

• ECSS SOLAR CONVERSION EFFICIENCY (CSCEF) 1s the ratio of the 
solar energy delivered to the load subsystems to the total energy 
incident on the collector array. 

ECSS OPERATING ENERGY (CSOPE) 1s the electrical operating energy 
required to support the ECSS heat transfer loops. 






A-1 



• TOTAL ENERGY CONSUMED (TECSM) is the sum of the collected solar 
energy, the total system operating energy, the total fossil fuel 
energy, and the total electrical fuel energy. This performance 
factor represents the total energy demands of the system from all 
outside sources. 

t SYSTEM PERFORMANCE FACTOR (SYSPF) is the ratio of the total system 
load to the equivalent fossil energy required to support the system 
for the month. The equivalent energy, as used in this context, is 
the sum of the actual fossil fuel (1/0.3) times the electrical 
requirements (for operating energy and fuel). This multiplication 
factor results from the estimation that, on the average, the effi- 
ciency of extracting fossil fuels from the ground, converting to 
electricity, and transmitting the electrical energy to the site is 
about 0.3. 

• LOAD is the amount of energy required for the month for each of the 
respective subsystems. 

• SOLAR FRACTION is the percentage of the load demand during the 
month for each subsystem which was supported by solar energy. 

• SOLAR ENERGY USED is the total amount of solar energy supplied 
each subsystem for the month. 

t AUXILIARY THERMAL USED is the amount of energy supplied, during 
the month, to the major components of each subsystem in the form 
of thermal energy in a heat transfer medium. This term also in- 
cludes the converted electrical fuel energy supplied to the sub- 
system. 

• AUXILIARY ELECTRICAL FUEL is the total amount of electrical energy 
supplied directly to each subsystem during the month. 



A-2 



ELECTRICAL ENERGY SAVINGS is the estimated difference between the 
electrical energy requirements of an alternative conventional sys- 
tem (carrying the full load) and the actual electrical energy 
required by each subsystem. 



SPACE HEATING SUBSYSTEM 

The space heating subsystem is characterized by an accounting of the energy 
flow into and from the subsystem. In addition, the savings 1n energy attri- 
butable to the use of solar energy are presented. 

• SPACE HEATING LOAD (HL) is the energy demand on the space heating 
subsystem, generally less than the building heating load. 

• SOLAR FRACTION OF LOAD (HSFR) is the percentage of the space heat- 
ing demand satisfied by solar energy. 

SOLAR ENERGY USED (HSE) is the amount of solar energy used by the 
space heating subsystem. 

t AUXILIARY THERMAL USED (HAT) is the amount of energy supplied to 

the major components of the subsystem in the form of thermal energy 

in a heat transfer fluid or its equivalent. This term includes the 

converted electrical and fossil fuel energy supplied to the subsys- 
tem. 

• AUXILIARY ELECTRICAL FUEL (HAE) is the amount of electrical energy 
supplied directly to the subsystem. 

t ELECTRICAL ENERGY SAVINGS (HSVE) is the estimated difference between 
the electrical energy requirements of an alternative conventional 
system (carrying the full load) and the actual electrical energy 
required by the subsystem. 



A-3 



• BUILDING TEMPERATURE (TB) Is the average heated space dry bulb 
temperature. 

• AMBIENT TEMPERATURE (TA) 1s the average ambient dry bulb tempera- 
ture at the site. 



ENVIRONMENTAL SUMMARY 

The environmental summary is a collection of the weather data which 1s 
generally instrumented at each site in the program. It is tabulated in this 
data report for two purposes — as a measure of the conditions prevalent 
during the operation of the system at the site, and as an historical record 
of weather data for the vicinity of the site. 

• TOTAL INSOLATION (SE) 1s accumulated total solar energy incident 
upon the gross collector array measured at the site. 

• AMBIENT TEMPERATURE (TA) 1s the average temperature of the envi- 
ronment at the site. 

• WIND DIRECTION (WDIR) 1s the average direction of the prevailing 
wind. 

• WIND SPEED (WIND) 1s the average wind speed measured at the site. 

• DAYTIME AMBIENT TEMPERATURE (TDA) 1s the temperature during the 
period from three hours before solar noon to three hours after 
solar noon. 

• RELATIVE HUMIDITY (RELH) 1s the average outside relative humidity. 



A-4 



PASSIVE SPACE HEATING 

In addition to the characterization of the space heating subsystem pre- 
viously mentioned, several other parameters are reported for passive space 
heating systems. 

• CHANGE IN STORED ENERGY (STECH) 1s the change in energy level of 
all components of the solar energy storage mass. 

• DIRECT SOLAR UTILIZATION EFFICIENCY (CSCEF) is the ratio of the 
solar energy used to the incident solar energy. 



PASSIVE SYSTEM ENVIRONMENT 

In addition to the environmental summary performance factors presented 
earlier, additional performance factors describing the interior environ- 
ment of a passive space heating system are presented. 

t BUILDING COMFORT ZONE 1 (COM!) is an index relating to the com- 
fort conditions on the south side of the building. The index 
is formed as an average of the average dry bulb and mean radiant 
temperatures inside the zone. 

• BUILDING COMFORT ZONE 2 (COM2) is an index relating to the comfort 
conditions on the north side of the building and is defined simi- 
larly to the other comfort index. 

• BUILDING TEMPERATURE MIDNIGHT (TMID) is the average building in- 
terior temperature at midnight local solar time. 

t BUILDING TEMPERATURE 6 A.M. (T6AM) is the average building interior 
temperature at 6 A.M. local solar time. 



A-5 



• BUILDING TEMPERATURE NOON (TNOON) is the average building 
interior temperature at local solar noon. 

• BUILDING TEMPERATURE 6 P.M. (T6PM) is the average building 
interior temperature at 6 P.M. local solar time. 

• INTERIOR RELATIVE HUMIDITY (RELHIN) is the average relative 
humidity inside the building. 

• AVERAGE STORAGE TEMPERATURE (TST) is the mass weighted average 
temperature of all solar storage masses. 



HULLCO SITE SPECIAL REPORT 

For the Hullco Construction Site, the average temperatures of all signifi- 
cant storage masses are presented. 

t ROCK STORAGE AVERAGE TEMPERATURE (TSTROCK) is the average tem- 
perature of the north side bed as measured by the twelve sensors 
in the rock bed. 

t TROMBE WALL AVERAGE TEMPERATURE (TSTWALL) is the average tempera- 
ture of the wall between the greenhouse and the house. 

§ DIRECT GAIN FLOOR AVERAGE TEMPERATURE (TSTFLOOR) is the average 
temperature of the concrete building slab floor near the south 
side of the building. 



A-6 



APPENDIX B 

SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS 

INTRODUCTION 

Solar energy system performance is evaluated by performing energy balance 
calculations on the system and its major subsystems. These calculations 
are based on physical measurement data taken from each subsystem every 320 
seconds. This data is then numerically combined to determine the hourly, 
daily, and monthly performance of the system. This appendix describes the 
general computational methods and the specific energy balance equations 
used for this evaluation. 

Data samples from the system measurements are numerically integrated to 
provide discrete approximations of the continuous functions which charac- 
terize the system's dynamic behavior. This numerical integration is 
performed by summation of the product of the measured rate of the appro- 
priate performance parameters and the sampling interval over the total time 
period of interest. 

There are several general forms of numerical integration equations which 
are applied to each site. These general forms are exemplified as follows: 
The total solar energy available to the collector array is given by 

SOLAR ENERGY AVAILABLE = (1/60) x I [1001 x AREA] x Ax 

where 1001 is the solar radiation measurement provided by the pyranometer 

2 
in Btu/ft -hr, AREA is the area of the collector array in square feet, Ax 

is the sampling interval in minutes, and the factor (1/60) is included to 

correct the solar radiation "rate" to the proper units of time. 

Similarly, the energy flow within a system is given typically by 

COLLECTED SOLAR ENERGY = z [W100 x CP x RH0 x (T150 -T100)] x Ax 



B-l 



where Wl 00 is the flow rate of the heat transfer fluid in gal/min, CP and 
RHO are the specific heat and density, and T100 and T150 are the tempera- 
tures of the fluid before and after passing through the heat exchanging 
component. Frequently this temperature difference is referred to as simply 
TD100. The product W100 x RHO 1s often combined and represented as Ml 00. 

For electrical power, a general example is 

ECSS OPERATING ENERGY = (3413/60) x I [EP100] x Ax 

where EP100 is the power required by electrical equipment in kilowatts and 
the two factors (1/60) and 3413 correct the data to Btu/m1n. 

These equations are comparable to those specified in "Thermal Data Require- 
ments and Performance Evaluation Procedures for the National Solar Heating 
and Cooling Demonstration Program" [2]. This document was prepared by an 
Inter-agency committee of the government, and presents guidelines for 
thermal performance evaluation. 

Performance factors are computed for each hour of the day. Each numerical 
Integration process, therefore, 1s performed over a period of one hour. 
Since long-term performance data 1s desired, 1t 1s necessary to build 
these hourly performance factors to daily values. This is accomplished, 
for energy parameters, by summing the 24 hourly values. For temperatures, 
the hourly values are averaged. Certain special factors, such as effi- 
ciencies, require appropriate handling to properly weight each hourly 
sample for the dally value computation. Similar procedures are required 
to convert dally values to monthly values. 

All energies are expressed 1n Btu's, while temperatures are expressed as 
degrees Fahrenheit. Efficiencies are expressed as dlmentlonless ratios. 

Location and definition of the measurements used are contained 1n Table 
4-1 of Section 4. 



B-2 



EQUATIONS USED IN MONTHLY REPORT 

AVERAGE AMBIENT TEMPERATURE 

TA = (1/60) x E T001 x At 

DAYTIME AVERAGE AMBIENT TEMPERATURE 
TDA = (1/360) x E T001 x At 

FOR + 3 HOURS FROM SOLAR NOON 

AVERAGE BUILDING TEMPERATURE 

TB = (1/300) x I (T600 + T601 + T602 + T603 + T604) x At 

TIME OF DAY BUILDING TEMPERATURES (ONCE PER DAY) 
TMID = TB 

AT 12 HOURS FROM LOCAL SOLAR NOON 
T6AM = TB 

AT 6 HOURS BEFORE LOCAL SOLAR NOON 
TNOON = TB 

AT LOCAL SOLAR NOON 
T6PM = TB 

AT 6 HOURS PAST LOCAL SOLAR NOON 

INCIDENT SOLAR ENERGY PER SQUARE FOOT 
SE = (1/60) x E 1001 x At 

AVERAGE ROCK STORAGE TEMPERATURE 

TSTROCK = (1/1080) x I (T200 + T201 + T202 + T203 + T204 + 

T205 + T206 + T207 + T208 + T209 + T210 + T211 + 

T212 + T213 + T214 + T215 + T216 + T217) x At 

AVERAGE FLOOR STORAGE TEMPERATURE 

TSTFLOOR = (1/600) x E (T218 + T219 + T221 + T222 + T224 + 
T225 + T227 + T228 + T245 + T246) x At 



B-3 



EQUATIONS USED IN MONTHLY REPORT (Continued) 

AVERAGE GREENHOUSE WALL STORAGE TEMPERATURE 

TSTWALL = (1/180) x I (T230 + T231 + T232) x At 

NORTH SIDE HEAT LOSS 

HLN = (1/60) x E [NOAREA x UWALL x (T235 - T234) + 

NGLASS x UGLASS x 0.5 x ((T600 + T601 ) - T001)] 

X At 

SOUTH SIDE HEAT LOSS 

HLS = (1/60) x E [SOAREA x USOUTH x (0.5 x (T100 + 
T101) - T001)] x At 

EAST SIDE HEAT LOSS 

HLE = (1/60) x E [GHAREA x UWALL x (T239 - T240) + 
EAAREA x UWALL x (R233 - T234) + EGLASS x 
UGLASS x (T604 - T001 )] x At 

WEST SIDE HEAT LOSS 

HLW = (1/60) x E [GHAREA x UWALL x (T239 - T240) + 
WEAREA x UWALL x (T237 - T238)] x At 

FLOOR HEAT LOSS 

HLF = (1/60) x E [FLAREA x UFLOOR x (TB - 0.2 x (T220 
+ T223 + T226 + T229 + T247))] x At 

ROOF HEAT LOSS 

HLC = (1/60) x I [ROAREA x UROOF x (TB - T001)] x At 

INFILTRATION HEAT LOSS 

NCHANGE = (1/60) x I [IC1 + IC2 x (TB - TA) + IC3 x 
V001] x At 

IN AIR CHANGES PER HOUR 



B-4 



EQUATIONS USED IN MONTHLY REPORT (Continued) 

HLI = NCHANGE x VOLUME x [H(TB) - H(TA)] x RHO 

IN BTU WHERE H IS AIR ENTHALPY FUNCTION AND RHO IS 
AIR DENSITY. 

ECSS OPERATING ENERGY 

CSOPE = (3413/60) x E (EP100 + EP101) x At 

WOOD STOVE ENERGY 

HFIRE = (1/60) x I FIRERATE x At 

IF THE WOOD STOVE IS OPERATING 

AUXILIARY ELECTRIC AND THERMAL ENERGIES 

HAE = (3413/240) x E (EP400 + EP401 + EP402 + EP403) x At 
HAT = HAE 

WIND DIRECTION AND VELOCITY (WDIR AND WIND) 

WNS = (1/60) x E V001 x COSINE (D001) x At 
WEW = (1/60) x E V001 x SINE (D001 ) x At 
WDIR = INVERSE TANGENT (WEW/WNS) 
WIND = (1/60) x E V001 x At 

ZONE 1 COMFORT INDEX 

C0M1 = (1/60) x Z 0.5 x [(T602 + T603 + T604)/3 + 
(T221 + T227 + T232)/3] x At 

ZONE 2 COMFORT INDEX 

COM2 = (1/60) x E 0.5 x (T600 + T601 ) x At 

INTERIOR RELATIVE HUMIDITY 

RELHIN = (1/60) x E RH600 x At 

EXTERIOR RELATIVE HUMIDITY 

RELH = (1/60) x E RH601 x At 



B-5 



SOLAR ENERGY TO SPACE HEATING SUBSYSTEM (BTU) 

HSE = STEO x STORSFR 
AUXILIARY THERMAL ENERGY TO SPACE HEATING SUBSYSTEM (BTU) 

HAT = STEO x [1 - STORSFR] + HAE x HPCOMPF 

WHERE HPCOMPF = HEAT PUMP COMPRESSOR EFFICIENCY (ASSUMED 
TO BE 0.7) 
INCIDENT SOLAR ENERGY ON COLLECTOR ARRAY (BTU) 

SEA = CLAREA x SE 
COLLECTED SOLAR ENERGY (BTU/FT 2 ) 

SEC = SECA/CLAREA 
COLLECTOR ARRAY EFFICIENCY 

CAREF = SECA/SEA 
CHANGE IN STORED ENERGY (BTU) 

STECH = STECH1 - STECH1 

WHERE THE SUBSCRIPT REFERS TO A PRIOR REFERENCE VALUE 
STORAGE EFFICIENCY 

STEFF = (STECH + STEO)/STEI 
SOLAR ENERGY TO LOAD SUBSYSTEMS (BTU) 

SEL = CSEO 
ECSS SOLAR CONVERSION EFFICIENCY 

CSCEF = SEL/SEA 
SPACE HEATING SUBSYSTEM SOLAR FRACTION (PERCENT) 

HSFR = 100 x HSE/HL 
SPACE HEATING SUBSYSTEM ELECTRICAL ENERGY SAVINGS (BTU) 

HSVE = CONV - HOPE 

WHERE CONV IS THE ELECTRICAL ENERGY REQUIRED FOR THE 
CONVENTIONAL SYSTEM. 



B-6 



EQUATIONS FOR MONTHLY REPORT (Continued) 



UNDER = UA x (68 - TB) 

IF TB IS LESS THAN 68 
FIRE = MINIMUM OF HFIRE AND OVER 
SETHSVE = COMHSVE - UNDER - (OVER - FIRE) 

TOTAL ENERGY CONSUMED 

TECSM = HSE + CSOPE + HAE + HFIRE 

AVERAGE SOLAR STORAGE TEMPERATURE 

TST = R1F x TSTROCK + R2F x TSTFLOOR + R3F x TSTWALL 

CHANGE IN LEVEL OF STORED SOLAR ENERGY 

STECH = TMROCK x (TSTROCK - TSTROCK ) + TMFLOOR x (TSTFLOOR 

TSTFLOOR ) + TMWALL x (TSTWALL - TSTWALL ) 
P P 

COLLECTED SOLAR ENERGY 

SECA = HSE + STECH 

COLLECTED SOLAR ENERGY PER UNIT COLLECTION AREA 

SEC = SECA/CLAREA 

ECSS SOLAR UTILIZATION EFFICIENCY 
CSCEF = SEL/SEA 



B-7 



*U.S. GOVERNMENT PRINTING OFFICE: 1980-640-189/4221. Region 4. 



UNIVERSITY OF FLORIDA 



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